C++11 thread_local destructors support

This feature is specifically for the C++ compiler to offload calling
thread_local object destructors on thread program exit, to glibc.
This is to overcome the possible complication of destructors of
thread_local objects getting called after the DSO in which they're
defined is unloaded by the dynamic linker.  The DSO is marked as
'unloadable' if it has a constructed thread_local object and marked as
'unloadable' again when all the constructed thread_local objects
defined in it are destroyed.

6 files changed, 266 insertions, 2 deletions

diff --git a/stdlib/Makefile b/stdlib/Makefile
index e2078f8877..6f98c71c64 100644
--- a/stdlib/Makefile
+++ b/stdlib/Makefile
@@ -34,7 +34,7 @@ routines	:=							      \
 	bsearch qsort msort						      \
 	getenv putenv setenv secure-getenv				      \
 	exit on_exit atexit cxa_atexit cxa_finalize old_atexit		      \
-	quick_exit at_quick_exit cxa_at_quick_exit			      \
+	quick_exit at_quick_exit cxa_at_quick_exit cxa_thread_atexit_impl     \
 	abs labs llabs							      \
 	div ldiv lldiv							      \
 	mblen mbstowcs mbtowc wcstombs wctomb				      \
@@ -71,9 +71,11 @@ tests		:= tst-strtol tst-strtod testmb testrand testsort testdiv   \
 		   tst-makecontext2 tst-strtod6 tst-unsetenv1		    \
 		   tst-makecontext3 bug-getcontext bug-fmtmsg1		    \
 		   tst-secure-getenv tst-strtod-overflow tst-strtod-round   \
-		   tst-tininess tst-strtod-underflow
+		   tst-tininess tst-strtod-underflow tst-tls-atexit
 tests-static	:= tst-secure-getenv
 
+modules-names	= tst-tls-atexit-lib
+
 include ../Makeconfig
 
 ifeq ($(build-shared),yes)
@@ -155,3 +157,9 @@ $(objpfx)bug-getcontext: $(link-libm)
 $(objpfx)tst-strtod-round: $(link-libm)
 $(objpfx)tst-tininess: $(link-libm)
 $(objpfx)tst-strtod-underflow: $(link-libm)
+
+tst-tls-atexit-lib.so-no-z-defs = yes
+
+LDFLAGS-tst-tls-atexit = $(common-objpfx)nptl/libpthread.so \
+			 $(common-objpfx)dlfcn/libdl.so
+$(objpfx)tst-tls-atexit.out: $(objpfx)tst-tls-atexit-lib.so
diff --git a/stdlib/Versions b/stdlib/Versions
index 250bd5fad7..f1777dfcf4 100644
--- a/stdlib/Versions
+++ b/stdlib/Versions
@@ -106,6 +106,9 @@ libc {
   GLIBC_2.17 {
     secure_getenv;
   }
+  GLIBC_2.18 {
+    __cxa_thread_atexit_impl;
+  }
   GLIBC_PRIVATE {
     # functions which have an additional interface since they are
     # are cancelable.
@@ -114,5 +117,6 @@ libc {
     __abort_msg;
     # Used from other libraries
     __libc_secure_getenv;
+    __call_tls_dtors;
   }
 }
diff --git a/stdlib/cxa_thread_atexit_impl.c b/stdlib/cxa_thread_atexit_impl.c
new file mode 100644
index 0000000000..9638efc7a0
--- /dev/null
+++ b/stdlib/cxa_thread_atexit_impl.c
@@ -0,0 +1,102 @@
+/* Register destructors for C++ TLS variables declared with thread_local.
+   Copyright (C) 2012 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <stdlib.h>
+#include <ldsodefs.h>
+
+typedef void (*dtor_func) (void *);
+
+struct dtor_list
+{
+  dtor_func func;
+  void *obj;
+  struct link_map *map;
+  struct dtor_list *next;
+};
+
+static __thread struct dtor_list *tls_dtor_list;
+static __thread void *dso_symbol_cache;
+static __thread struct link_map *lm_cache;
+
+/* Register a destructor for TLS variables declared with the 'thread_local'
+   keyword.  This function is only called from code generated by the C++
+   compiler.  FUNC is the destructor function and OBJ is the object to be
+   passed to the destructor.  DSO_SYMBOL is the __dso_handle symbol that each
+   DSO has at a unique address in its map, added from crtbegin.o during the
+   linking phase.  */
+int
+__cxa_thread_atexit_impl (dtor_func func, void *obj, void *dso_symbol)
+{
+  /* Prepend.  */
+  struct dtor_list *new = calloc (1, sizeof (struct dtor_list));
+  new->func = func;
+  new->obj = obj;
+  new->next = tls_dtor_list;
+  tls_dtor_list = new;
+
+  /* See if we already encountered the DSO.  */
+  __rtld_lock_lock_recursive (GL(dl_load_lock));
+
+  if (__builtin_expect (dso_symbol_cache != dso_symbol, 0))
+    {
+      ElfW(Addr) caller = (ElfW(Addr)) dso_symbol;
+
+      struct link_map *l = _dl_find_dso_for_object (caller);
+
+      /* If the address is not recognized the call comes from the main
+         program (we hope).  */
+      lm_cache = l ? l : GL(dl_ns)[LM_ID_BASE]._ns_loaded;
+    }
+  /* A destructor could result in a thread_local construction and the former
+     could have cleared the flag.  */
+  if (lm_cache->l_type == lt_loaded && lm_cache->l_tls_dtor_count == 0)
+    lm_cache->l_flags_1 |= DF_1_NODELETE;
+
+  new->map = lm_cache;
+  new->map->l_tls_dtor_count++;
+
+  __rtld_lock_unlock_recursive (GL(dl_load_lock));
+
+  return 0;
+}
+
+/* Call the destructors.  This is called either when a thread returns from the
+   initial function or when the process exits via the exit(3) function.  */
+void
+__call_tls_dtors (void)
+{
+  while (tls_dtor_list)
+    {
+      struct dtor_list *cur = tls_dtor_list;
+      tls_dtor_list = tls_dtor_list->next;
+
+      cur->func (cur->obj);
+
+      __rtld_lock_lock_recursive (GL(dl_load_lock));
+
+      /* Allow DSO unload if count drops to zero.  */
+      cur->map->l_tls_dtor_count--;
+      if (cur->map->l_tls_dtor_count == 0 && cur->map->l_type == lt_loaded)
+        cur->map->l_flags_1 &= ~DF_1_NODELETE;
+
+      __rtld_lock_unlock_recursive (GL(dl_load_lock));
+
+      free (cur);
+    }
+}
+libc_hidden_def (__call_tls_dtors)
diff --git a/stdlib/exit.c b/stdlib/exit.c
index e9a2139f4e..2e86caa2d4 100644
--- a/stdlib/exit.c
+++ b/stdlib/exit.c
@@ -33,6 +33,9 @@ attribute_hidden
 __run_exit_handlers (int status, struct exit_function_list **listp,
 		     bool run_list_atexit)
 {
+  /* First, call the TLS destructors.  */
+  __call_tls_dtors ();
+
   /* We do it this way to handle recursive calls to exit () made by
      the functions registered with `atexit' and `on_exit'. We call
      everyone on the list and use the status value in the last
diff --git a/stdlib/tst-tls-atexit-lib.c b/stdlib/tst-tls-atexit-lib.c
new file mode 100644
index 0000000000..aab28bb607
--- /dev/null
+++ b/stdlib/tst-tls-atexit-lib.c
@@ -0,0 +1,36 @@
+/* Verify that DSO is unloaded only if its TLS objects are destroyed - the DSO.
+   Copyright (C) 2012 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+extern void *__dso_handle;
+
+typedef struct
+{
+  void *val;
+} A;
+
+/* We only care about the destructor.  */
+void A_dtor (void *obj)
+{
+  ((A *)obj)->val = obj;
+}
+
+void do_foo (void)
+{
+  static __thread A b;
+  __cxa_thread_atexit_impl (A_dtor, &b, __dso_handle);
+}
diff --git a/stdlib/tst-tls-atexit.c b/stdlib/tst-tls-atexit.c
new file mode 100644
index 0000000000..b7312cbc84
--- /dev/null
+++ b/stdlib/tst-tls-atexit.c
@@ -0,0 +1,111 @@
+/* Verify that DSO is unloaded only if its TLS objects are destroyed.
+   Copyright (C) 2012 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+/* There are two tests in this test case.  The first is implicit where it is
+   assumed that the destructor call on exit of the LOAD function does not
+   segfault.  The other is a verification that after the thread has exited, a
+   dlclose will unload the DSO.  */
+
+#include <dlfcn.h>
+#include <pthread.h>
+#include <stdio.h>
+#include <unistd.h>
+#include <string.h>
+#include <errno.h>
+
+void *handle;
+pthread_mutex_t m = PTHREAD_MUTEX_INITIALIZER;
+
+void *
+load (void *u)
+{
+  pthread_mutex_lock (&m);
+  handle = dlopen ("$ORIGIN/tst-tls-atexit-lib.so", RTLD_LAZY);
+  if (!handle)
+    {
+      printf ("Unable to load DSO: %s\n", dlerror ());
+      return (void *) (uintptr_t) 1;
+    }
+
+  void (*foo) (void) = (void (*) (void)) dlsym(handle, "do_foo");
+
+  if (!foo)
+    {
+      printf ("Unable to find symbol: %s\n", dlerror ());
+      exit (1);
+    }
+
+  foo ();
+
+  /* This should not unload the DSO.  If it does, then the thread exit will
+     result in a segfault.  */
+  dlclose (handle);
+  pthread_mutex_unlock (&m);
+
+  return NULL;
+}
+
+int
+main (void)
+{
+  pthread_t t;
+  int ret;
+  void *thr_ret;
+
+  if ((ret = pthread_create (&t, NULL, load, NULL)) != 0)
+    {
+      printf ("pthread_create failed: %s\n", strerror (ret));
+      return 1;
+    }
+
+  if ((ret = pthread_join (t, &thr_ret)) != 0)
+    {
+      printf ("pthread_create failed: %s\n", strerror (ret));
+      return 1;
+    }
+
+  if (thr_ret != NULL)
+    return 1;
+
+  /* Now this should unload the DSO.  */
+  dlclose (handle);
+
+  /* Run through our maps and ensure that the DSO is unloaded.  */
+  FILE *f = fopen ("/proc/self/maps", "r");
+
+  if (f == NULL)
+    {
+      perror ("Failed to open /proc/self/maps");
+      fprintf (stderr, "Skipping verification of DSO unload\n");
+      return 0;
+    }
+
+  char *line = NULL;
+  size_t s = 0;
+  while (getline (&line, &s, f) > 0)
+    {
+      if (strstr (line, "tst-tls-atexit-lib.so"))
+        {
+	  printf ("DSO not unloaded yet:\n%s", line);
+	  return 1;
+	}
+    }
+  free (line);
+
+  return 0;
+}